Electrical heater and method of making the same



Jan. 27, 1970 s. A. OAKLEY ELECTRICAL HEATER AND METHOD OF MAKING THE SAME Filed Ju 7 67 5 m 4 m V W MA M mv TK m M m u #11 W United States Patent US. Cl. 338-296 7 Claims ABSTRACT OF THE DISCLOSURE There is provided a terminal structure for an electric heater. The terminal structure includes a terminal member provided with a plurality of longitudinally extending radial projections inserted within the helical end of a high resistance conductor, the radial projections being welded to the metallic conductor.

This invention relates to electric heaters, and particularly to electric heaters of the type which include a high resistance metallic conductor having a terminal member attached thereto, and more particularly to an improved terminal member and method of joining the member to the conductor.

While the invention has general application, it is particularly useful in connection with electric heaters of the sheath-wire type wherein a resistance conductor is encased in a metallic sheath and is supported in spaced relation within the sheath by a compacted mass of powdered heat conducting and electrically insulating material, such as magnesium oxide.

It is common in a heater of the sheath-wire type to provide a terminal structure which consists of a terminal member inserted within the helically wound end of a high resistance metallic conductor. The conductor and terminal member are commonly joined by welding, for example, in the manner described in my earlier US. patents, No. 2,546,215 and No. 2,890,320. Such prior constructions have been entirely satisfactory with many compositions of resistance wire and terminal members.

However, difficulty has been experienced with the weldof certain conductors, such as those formed of ironaluminum alloy and known under the trade name of Kanthal. Iron-aluminum alloys are destroyed if too great a welding heat is applied to them. It is believed that the aluminum separates from the alloy and comes to the surface where an aluminum oxide is formed which is difficult to Weld. Therefore, the present invention is particularly advantageous in joining terminal members to con ductors formed of iron-aluminum alloy, but may also be used with conductors of other materials, such as of chrome-nickel alloy.

Accordingly, it is an object of the present invention to provide a new and improved electric heater structure.

Another object of the present invention is to provide a new and improved terminal member for use with an electric heating structure.

Yet another object of the present invention resides in the provision of a new and improved terminal member which is particularly advantageous for welding to ironaluminum alloyed conductors.

Yet a further object of the present invention is the provision of a new and improved method of joining a terminal to an electric heating structure.

Further objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

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In accordance with these and other objects, there is provided an improved terminal member for use with an electric" heater structure of the type including a high resistance metallic conductor having an end portion thereof formed in a helix. The terminal member includes a connecting portion formed at one thereon defined by a plurality of longitudinally extending radial projections. The connecting portion may be inserted into the helical end portion of the conductor and welded therewith. The projections of the terminal will weld to the helical turns of the conductor to provide a mechanically and electrically 4 satisfactory connection.

In accordance with another feature of the present invention,there is provided an improved method of making a terminal connection to an electric heating structure of the type described above and including the formation of a helical end portion to a high resistance conductor, and the formation of a connecting portion at one end of a terminal member defining a plurality of longitudinally extending radial projections. The terminal member is then inserted into the end portion of the conductor and the projections of the terminal member are welded to the conductor. It has been found that electric percussion welding by the application of a heavy impact of current for a short period of time provides optimum results. With the projection welding, the projections on the terminal members come up to welding temperature very rapidly, and the wire notches into the projections to provide point contact. The points get very hot and transfer the heat to the terminal member and conductor without damaging the iron-aluminum material of the conductor.

It has been found that a terminal applied by the present method requires fifteen to one hundred pounds pull to pull the terminal member from the conductor, whereas prior art terminal members applied to the same conductor would pull off with a five to ten pound pull.

For a better understanding of the present invention reference may be had to the accompanying drawings wherein:

FIG. 1 is a partial sectional view of an electric heater structure according to the present invention;

FIG. 2 is a somewhat schematic illustration of an electric heater structure illustrating the welding operation thereon;

FIG. 3 is a cross sectional view of the structure of FIG. 2, taken along line 3-3 thereof; FIG. 4 is a cross sectional view of an electric heater structure according to another embodiment of the present invention; and FIG. 5 is a cross sectional view of an electric heater structure according to yet another embodiment of the present invention.

Referring now to the drawings, and particularly to FIG. 1 thereof, there is illustrated an electric heater structure 10 according to the present invention and including a high resistance metallic conductor 11 encased in a metallic sheath 12 and supported in spaced relation therewith by a compacted mass of powdered heat conducting and electrically insulating material 13 such as magnesium oxide. A terminal member 14 is joined to each end of the conductor 11 and extends out of the sheath 12 to provide for electrical connection of the conductor 11 with an external circuit. As best illustrated in FIGS. 2 and 3, the conductor 11 of the electric heater structure 10 has an end portion 11a thereof formed in a helix. The terminal member 14 has an end connecting portion 14a inserted into the helix 11a thereby joining the conductor 11 and terminal member 14. In accordance with the present invention, the end connecting portion 14a is provided with a plurality of longitudinally extending radial projections 1411, here defined as knurls, engaging the conductor 11. If desired, the end connecting portion 14a may be tapered toward its end,as illustrated in FIG. 2,

to provide good contact with the helix 11a.

The terminal members 14 are welded to the conductors 11 in the manner illustrated in FIG. 2. More specifically there is provided one or more welding electrodes or jaws 18, here illustrated as a pair, movable to clamp against the helix 11a of the conductor 11, and the remainder of the terminal member 14 defines a negative electrode through engagement with welding electrodes 19. The welding electrodes 18 have the same radius and. shape as the outer surface of the helix 11a to provide for good contact over a large area. The welding circuit interconnecting the electrodes 18 and 19 may be of the type defined in my earlier patents referenced above. An application of welding currentis effective to cause the projections 14b to weld with the turns of the conductor 11 in the helix 11a.

It has been found that twenty knurls on a .091 terminal member, when inserted within the helix of a .015 iron-aluminum wire, provides an excellent weld with four hundred amperes welding current. The point contact between the projections 14b and the conductor 11 provides very hot spots due to localization of the welding current along these paths, and provides a satisfactory weld without destroying the iron-aluminum conductor.

Referring now to the embodiment of FIG. 4, there is illustrated a terminal member having an end connecting portion triangular in cross section. More specifically there is provided a terminal member 22 having an end projecting portion 22a inserted within an end helical portion 11a of a conductor, such as conductor 11 heretofore described. The end connecting portion 22a is triangular in cross section and defines a plurality of longitudinally extending radial projections 22b at the respective corners of the triangle. These projections 22b form small areas of virtually point contact with the helix 11a and consequently function in like manner as the projections 14b of the embodiment of FIGS. 1 through 3. The terminal structure may be clamped and welded between suitable welding electrodes, such as the electrodes 18.

In the embodiment of FIG. 5, the terminal member is provided with an end connecting portion which is a regular polygon in cross section. More specifically there is provided a heater structure including the conductor having the helical end portion 11a, and a terminal member 24 having an end connecting portion 24a which is polygonal in cross section so as to define a plurality of longitudinally extending radial projections 24b. In the illustrated embodiment the polygonal cross section is of regular sixsided shape to provide six projections 24b. When inserted within the helix 11a, as illustrated in FIG. 5, the projections 24b may be clamped and welded to the helix 11a by the'application of welding current to the electrodes 18.

The present invention is also directed to the method of making a terminal connection to an electric heating structure of the type described wherein a terminal member is joined to a high resistance metallic conductor. More specifically, the conductor 11 is formed with a helix 11a on one end portion thereof and the terminal member 14 is formed with an end connecting portion 14a at one end thereof. The formation of the end connecting portion 14 includes the formation of a plurality of longitudinally extending radial projections 14b thereon. In the illustrated embodiment, the projections 14b are formed by knurling on the outer surface of the end connecting portion 14a. Thereafter the end connecting portion 14a of the terminal member 14 is inserted within the helix 11a. The helix 11a is clamped by the welding electrodes or jaws 18 and a welding current is passed through the jaws 18 and into the terminal member 14 which is maintained at ground potential by the terminals 19. It has been found that percussion welding by the application of a heavy impact of current for a short period of time provides an excellent bond, both mechanically and electrically, between the terminal member 14 and the helix 11a.

Although the present invention has been described by reference to several embodiments thereof, it will be apparent that numerous other modifications and embodiments may be devised by those skilled in the art and it is intended by the appended claims to cover all such modifications and embodiments as fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. An electric heater structure including a high resistance metallic conductor having an end portion thereof formed in a helix, a terminal member including a connecting portion formed at one end of said terminal member defined by a plurality of longitudinally extending radial projections, said connecting portion being inserted into said end portion with said radial projections being welded to said metallic conductor.

2. An electric heating structure as defined in claim 1 wherein said conductor is formed of an iron-aluminum alloy.

3. An electric heater structure as defined in claim 1 wherein said radial projections are defined by knurls.

4. An electric heater structure as defined in claim 1 wherein said connecting portion is triangular in cross section, the angles of the triangle defining said radial projections.

5. An electric heater structure as defined in claim 1 wherein said connecting portion is of regular polygonal cross section, the angles of the polygon defining said radial projections.

6. The method of making a terminal connection to an electric heating structure of the type including a high resistance metallic conductor and a terminal member, said method comprising the steps of forming a helix on an end portion of a conductor, forming a connecting portion at one end of a terminal member including forming a plurality of longitudinally extending radial projections on said connecting portion, inserting the connecting portion into the end portion of a conductor, and welding the projection of the conductor.

7. The method of making a terminal connection as set forth in claim6 wherein the last step includes electric percussion welding by the application of a heavy impact of current for a short period of time.

References Cited UNITED STATES PATENTS ELLIOT A. GOLDBERG, Primary Examiner U.S. Cl. X.R. 

